def __init__(self, formula):
'''
Constructor
formula -- the formula to parse
'''
self.lexer = ChemicalLexer(formula)
self.formula = GroupingNode()
self.group_stack = []
class ChemicalParser(object):
'''
Parser for chemical formulas. the
output is a dict of elements in the formula
and their quantities.
'''
def __init__(self, formula):
'''
Constructor
formula -- the formula to parse
'''
self.lexer = ChemicalLexer(formula)
self.formula = GroupingNode()
self.group_stack = []
def current_group(self):
'''
Get the current group, either from the stack
or self.formula if the stack is empty
'''
try:
return self.group_stack[-1]
except IndexError:
return self.formula
def element(self, token):
'''
Add an element to the current group
'''
node = ElementNode(token.value)
group = self.current_group()
group.add(node)
def quantity(self, token):
'''
Quantify the most recent group or element node
added to the current group
'''
node = self.current_group().last()
if node:
node.quantity = int(token.value)
else:
raise Exception("Missing Atom before quantifier {}".format(token.value))
def left_grouping(self, token):
'''
When a left grouping symbol is encountered,
push a new subformula onto the stack
'''
node = GroupingNode(token.value)
self.group_stack.append(node)
def right_grouping(self, token):
'''
When a right grouping symbol is encountered, this subformula is complete.
pop the current subformula off the stack and add it
to the subformula that is the new top of the stack.
'''
group = self.current_group()
if group.closing_symbol() == token.value:
node = self.group_stack.pop()
group = self.current_group()
group.add(node)
else:
raise Exception("Missing Grouping Symbol {}".format(group.closing_symbol()))
def parse(self):
'''
Run the lexer and parse each token.
self.formula will then contain a GroupingNode tree that represents
the whole formula
returns self.formula.get_atoms_dict()
'''
for token in self.lexer.token_gen():
if token.tag == 'ELEMENT':
self.element(token)
elif token.tag == 'QUANTITY':
self.quantity(token)
elif token.tag == 'LEFT_GROUPING':
self.left_grouping(token)
elif token.tag == 'RIGHT_GROUPING':
self.right_grouping(token)
else:
raise Exception("Invalid Token {}".format(token))
if self.group_stack:
raise Exception("Missing Grouping Symbol {}".format(self.current_group().closing_symbol()))
return self.formula
